The constant pressure separatory funnel is a type of separatory funnel. Like other separatory funnels, it can perform operations such as liquid separation and extraction. Unlike other separatory funnels, the constant pressure separatory funnel maintains a constant internal pressure. This serves three purposes: first, it prevents backflow; second, it allows the liquid in the funnel to flow out smoothly; third, it minimizes the impact of added liquid on gas pressure, thereby ensuring greater accuracy when measuring gas volume.

PFA material constant pressure separatory funnels are resistant to acids, alkalis, and corrosion, especially hydrofluoric acid.